Revert "mm: introduce VM_POPULATE flag to better deal with racy userspace programs"

This reverts commit 186930500985 ("mm: introduce VM_POPULATE flag to
better deal with racy userspace programs").

VM_POPULATE only has any effect when userspace plays racy games with
vmas by trying to unmap and remap memory regions that mmap or mlock are
operating on.

Also, the only effect of VM_POPULATE when userspace plays such games is
that it avoids populating new memory regions that get remapped into the
address range that was being operated on by the original mmap or mlock
calls.

Let's remove VM_POPULATE as there isn't any strong argument to mandate a
new vm_flag.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 10 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 4723ac8d2fc2..87da3590c61e 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -204,10 +204,8 @@ get_write_lock:
                         unsigned long addr;
                         struct file *file = get_file(vma->vm_file);
 
-                        vm_flags = vma->vm_flags;
-                        if (!(flags & MAP_NONBLOCK))
-                                vm_flags |= VM_POPULATE;
-                        addr = mmap_region(file, start, size, vm_flags, pgoff);
+                        addr = mmap_region(file, start, size,
+                                        vma->vm_flags, pgoff);
                         fput(file);
                         if (IS_ERR_VALUE(addr)) {
                                 err = addr;
@@ -226,12 +224,6 @@ get_write_lock:
                 mutex_unlock(&mapping->i_mmap_mutex);
         }
 
-        if (!(flags & MAP_NONBLOCK) && !(vma->vm_flags & VM_POPULATE)) {
-                if (!has_write_lock)
-                        goto get_write_lock;
-                vma->vm_flags |= VM_POPULATE;
-        }
-
         if (vma->vm_flags & VM_LOCKED) {
                 /*
                  * drop PG_Mlocked flag for over-mapped range